Gst invoice & eway bill

 In Petroleum Exploration and Production Company, equipment and items are imported and kept in Centralised Stores (GRV raised). These items are then sent to a Drill site (Mine under Mines Act) for use and may either come back to the Stores after use or sent to another Drill site for use there. All locations are within 1 state and items are used for operations of the company only. Each of the transportation is by hired truck and the inter location distance is more than 10 kms. Do we need to generate GST Invoice and eWay Bill for each movement? And how to provide estimatedvalue of the equipment / item after each use? Is there any exemptions in the rules for such scenarios?